Electrostatographic pressure sensitive polymeric toner

ABSTRACT

A PRESSURE FIXABLE TONER COMPRISED OF A WEAKLY CROSSLINKED POLYMER THE CROSSLINK BONDS OF WHICH ARE DISRUPTED AND/OR BROKEN BY THE APPLICATION OF PRESSURE WHEREBY THE POLYMER IS SUFFICIENTLY SOFT TO BE FIXED BY PRESSURE.

United St te 1 ABSTRACT OF THE DISCLOSURE A pressure-fixable toner comprised of a weaklyv cross: linked amorphous polymer the crosslink bonds of which are disrupted and/or broken by the application of pressure whereby the polymer is sufficiently soft to be fixed by pressure.

This invention relates to electrostatography, and more particularly to improved electrostatographic developing materials and the use thereof.

Electrostatography is best exemplified by electrophotography. The basic electrophoto'graphic process, astaught by C. F. Carlson in U.S. Pat. 2,297,691, involves placing a uniform electrostatic charge on a photoconductive in-' sulating layer, exposing the layer to a light-and-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely divided electroscopic material referred to in the art as toner. The toner 'will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently aflixed to the support surface as by heat. Instead of latent image formation by uniformly charging the photoconductive layer and then exposing the layer to a light-and-shadow image, one may form the latent image by directly charging the layer in image configuration. The powder image may be fixed to the photoconductive layer if elimination '-of the powder image transfer step is desired. Other suitable fixing means such as solvent or overcoating treatment may be substituted for the foregoing heat fixing steps.

Final copies of the toner-image are generally prepared by heating the toner image on a suitable support to a temperature at which the toner flows in order to effect fusing of the toner to the support medium. In order to increase the speed at which toners may. be fixed to a support attempts have been made to form toners of low molecular weight resins which are easily heat fused at relatively low temperatures, but such attempts have not generally been successful in that such toners tend to block at low temperatures. Accordingly, there is a need: for new toners which can be fixed rapidly, and which have the physical properties required to withstand the conditions which are employed in the developing process,

An object of the invention is to provide an improved electrostatographic developer. I

Another object of this invention is to provide a toner which can be fixed rapidly and which has the physical properties required to withstand the conditions encountered in the developing process.

A further object of this invention is to provide a toner which is capable of being fixed to a support surface by the application of pressure.

These and other objects of the invention should be apparent from reading the following detailed. description thereof.

The objects of this invention are broadly accomplished by providing an electrostatographic toner of a finely divided colored resinous material in which the resinous 3,804,764 Patented Apr. 16, 1974 material includes a Weakly crosslinked amorphous polymer having a glass transition temperature (T of greater than about -20 C. The crosslinks of the polymer, as a result of their weakness, are shear sensitive and can be temporarily disrupted and/or broken by the application of pressure, resulting in a polymer which has the properties of the uncrosslinked polymer. Upon release of the pressure, the polymer reverts to its crosslinked state. Accordingly, such a toner is capable of being fixed to a support medium in image configuration, by the application of pressure.

The weakly crosslinked polymer is produced from a polymer having a T of less than 40 C., with the increase in T exhibited by the crosslinked polymer resulting from the production of the crosslinks. The toners of the present invention are capable of being fixed to a final copy by the application of pressure.

More particularly, the uncrosslinked polymer (commonly referred to as a prepolymer) from which the weakly crosslinked polymer is prepared is an amorphous polymer which has a T; from about 100 C. to about 40 C., preferably from about C. to about 20 C. It is to be understood, however, that these specified lower T limits are only exemplary of the starting materials employed in that polymers with a T lower than 100 C. can be employed, provided the weakly crosslinked polymer produced therefrom has the specified T The polymer molecular weight (number average) of the uncrosslinked polymer is generally from about 500 to about 100,000 preferably from about 1,000 to about 50,000 and includes more than two crosslink sites per molecule (functionality of molecule is greater than two) which are reactable to provide crosslinks having a bond strength from about 2 to about 30 kcaL/mole, and preferably bond strengths from about 3 to about 15 kcaL/mole. The T of the prepolymer and the number of crosslink sites therein are such that, upon crosslinking, the T of the crosslinked polymer mers'which are used in producing the toners of the present invention to provide a pressure fixable toner, the molecular weight, crosslink bond strength and glass transition temperature is selected within the specified ranges to provide a'polymer having a yield stress sufficiently low to permit yielding by the application of pressure. In general, the weakly crosslinked amorphous polymers which are suitable for the purposes of the present invention have a yield stress from about 500 to about 20,000 p.s.i., and preferably a yield stress from about 1,000 to about 5,000 p.s.1.

The weak crosslinks of the polymers which are suitable for the purposes of the present invention are formed by associative bonding (as opposed to covalent bonding), and as representative examples of types of associative bonding there may be mentioned: hydrogen bonding; ionic clustering (sometimes referred to as ionic crosslinking with such weakly crosslinked polymers sometimes being referred to as ionic polymers or ionomers, with the term ionic polymer as used herein referring to such weakly crosslinked polymers); metal coordinate bonding (including but not limited to chelates); and weak acid-weak base bonding (including but not limited to Lewis Acid-Bronsted Base bonding).

As representative examples of weakly crosslinked polymers in which the crosslink is formed by hydrogen bonding there may be mentioned: polymers including a carboxylic acid group, phenolic groups, amine groups, amide groups and the like. As representative examples of specific polymers which have hydrogen bonding and are suitable for the purposes of the present invention, there may be mentioned: a copolymer of n-butylmethacrylate and acrylic acid; a copolymer of vinyl n-alkyl pyridine and hexylmethacrylate; a copolymer of diacetone acrylamide and butyl acrylate; poly(N,N diisobutylhexamethyleneadipamide) and the like.

As representative examples of weakly crosslinked polymers in which the crosslink is formed by metal coordinate bonding, there may be mentioned: polymers which include functional groups capable of forming a bond with a metal having a valency greater than one, with such functional groups generally being either a carbonyl group, an ether group, a thio ether group, an amino group, an amide group and the like.

Weak acid-weak base associative bonding results from a single polymer which includes both acid and base groups or a polymer mixture which includes both acid and base groups, with the acidic functionality being exemplified by one or more of the following groups: carboxylic acids, boric acids, sulfonic acids, phosphonic acids, sulfinic acids and the like. The basic functionality groups are exemplified by one or more of the following groups: hydroxyl, pyridyl, amino and the like. As representative examples of weakly crosslinked polymers in which the associative bonding results from weak acidweak base bonding there may be mentioned: vinyl alcohol-vinyl acetate copolymer admixed with boric acid; vinyl pyridine-acrylic acid-butyl acrylate terpolymer and the like.

The ionic crosslinkages or clusterings are formed, as known in the art, by the polymer including a negative and/or positively charged group(s) either pendant to the polymer backbone, incorporated into the polymer backbone, or terminal to the polymer backbone, which is neutralized by an oppositely charged group to provide the ionic crosslink or cluster.

As representative examples of amorphous ionic polymers there may be mentioned polymers which include: as negatively charged groups, either free carboxylate groups (000-), free sulfonate groups (-O S), or phosphate groups, which may be neutralized with a metal cation or an amino cation etc.; or as a positively charged group, a free amino group, which may be neutralized with either a carboxylate group, an acid halide, in particular an acid chloride or bromide, a sulfonate group, etc. It is to be understood that the polymer may be formed with both negatively and positively charged groups to produce the ionic crosslink or cluster or the polymer may be fonmed with either a negatively or positively charged group and subsequently neutralized. It is also to be understood that the negatively and/or positively charged group may be pendant to the polymer backbone, incorporated into the polymer backbone or terminal to the polymer backbone, the aforesaid terminal group being derived either from the monomer(s) used in preparing the polymer or subsequently added as a terminal group to the polymer, as known in the art. The following structurally illustrates these various ionomer types:

4. I e.g., n-butyl methacrylate/vinyl n-methyl pyridinium chloride.

I NCH;

e.g., n-butyl methacrylate/vinyl n-methylpyridinium acid. 4) Na+-OOC OOO-Na+ e.g., carboxylic acid terminated n-butylmethacrylate homopolymer neutralized with sodium. It is to be understood that in polymers of this type more than two acid groups are associated with each sodium ion to produce a crosslink network.

e.g., diamino terminated amorphous polyamide neutralized with hydrochloric acid. It is to be understood that in polymers of this type more than two amino groups are associated with each chloride ion to produce a crosslink network.

It is also to be understood that a mixture of a polymer containing a negatively charged group and a polymer containing a positively charged group may be employed to provide the ionic crosslink.

The degree of neutralization of the polymer; i.e., the amount of ionic crosslinking or clustering, aifects the glass transition temperature of the ionic polymer and'the degree of neutralization of the prepolymer is controlled to provide an ionic polymer having a glass transition temperature, as hereabove described. It is also to be understood that the quantity of metal cation employed may also effect the humidity sensitivity and conductivity of the polymer, with an increase in the cation content making the ionic polymer more sensitive to moisture.

The monomers which are used in producing the weakly crosslinked polymers of the present invention, and in particular the ionic polymers, may be homopolymerized or copolymerized to provide a polymer having the required T It is to be understood that monomers which are known to homopolymerize to polymers having a T in excess of those suitable for the purposes of the present invention may also be employed as comonomers in that by properly selecting the other comonomer(s), as known in the art, a copolymer can be produced with the required T i.e., the copolymer has a T intermediate the T s of each of the homopolymers produced from such polymers and by selecting the monomers and the proportions thereof, a copolymer with the required T may be produced. As representative examples of monomers which are suitable for the purposes of the present invention there may be mentioned: styrenes, such as styrene, chlorostyrene, a-methyl styrene; alkyl methacrylates, wherein the alkyl group has 1-3 carbon atoms, such as methyl methacrylate, ethyl methacrylate; aminoalkylmethacrylates wherein the alkyl has 1-6 carbon atoms; acrylonitrile; vinyl acetate; vinyl chloride; acrylic acid; methacrylic acid and n-alkyl vinyl pyridinium salt; which are preferably copolymerized with one or more of the following monomers: alkyl acrylates where the alkyl group contains 1-12 C atoms; alkyl methacrylates where the alkyl group contains 4-12 C atoms, e.g. methyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-butyl methacrylate, lauryl methacrylate; vinylidene chloride and the like.

Condensation monomers include dicarboxylic acids, diols, diamines, di-isocyanates, etc. Examples are adipic acid, dimer acid, commercialized as Empol 1010 (Emerey Industries) or Versadyme (General Mills), hexamethylene diamine, dimer diamine and dimer diisocyanate (DDI) commercialized by General Mills, hexanediol, etc. and the like.

As representative examples of polymers which are suitable for the purposes of the present invention, in particular for the production of ionic polymers, there may be mentioned: poly(ethyl acrylate); styrene/n-butyl methacrylate; styrene/ ethyl acrylate; acrylonitrile/n-butyl acrylate; methyl methacrylate/methyl acrylate; vinyl chloride/methyl acrylate; ethyl methacrylate/vinylidene chloride; n-methyl vinyl pyridinium salt/n-butyl methacrylate; acrylic acid/n-butyl methacrylate; poly-N,N diisobutylhexamethylene sebacamide; poly-2,2,4-trimethyl hexamethylene adipate, 2,2,4 trimethylhexamethylene adipamide.

The procedures for preparing such polymers are known in the art, and no detailed explanation thereof is deemed necessary for a full understanding of the present invention.

The production of ionic polymers, i.e., the formation of ionic crosslinks or ionic clusters, is also performed as known in the art, e.g., note US. Pat. No. 3,264,272 which describes neutralization procedures for producing ionic crosslinks or clusters. The metal ions which are generally employed for producing the ionic crosslinks or clusters are the mono-, diand trivalent ions of metals in Groups I, II, III, IV-A and VIII of the Periodic Table of Elements (see page 392, Handbook of Chemistry and Physics, Chemical Rubber Publishing Co., 37th ed.). Suitable monovalent metal ions are Na+, K+, Li+, Cs+, Ag Hg+ and Cu Suitable divalent metal ions are Be, Mg, Ca, Sr, Ba+ Cu+ Cd, Hg, Sn, Pb- Fe Co, Ni+ and Zn. Suitable trivalent metal ions are Al+ Sc+ Fe+ and Y+ As representative examples of suitable anions for neutralizing cationic groups, there may be mentioned chloride, bromide, iodide, fluoride, sulfate, nitrate, borofiuoride, chromate, chloroplatinate, methane sulfonate, toluene sulfonate, acetate, propionate, etc. These anions are introduced into the ionomer by neutralizing the basic polymers with the corresponding acids, hydrochloride, hydrobromic, etc., either in solution or by a milling procedure.

The use of a weakly crosslinked polymer, as hereinabove described, in a toner is advantageous in that such a toner is capable of being pressure fixed and also has the properties desired for storage and use of the toner; i.e., resistance to impactation and blocking. Although the present invention is not limited to any theoretical reasons it is believed that the polymer, in its crosslinked state, provides sufiicient toughness to resist impactation and blocking, and upon application of pressure, which effects disruption or breaking of the crosslinks, the polymer is sufiiciently soft to be deformed and affixed to a suitable support member. Upon release of the pressure, the crosslinks are reestablished, and the deformed polymer, in image configuration, is retained on the support medium.

The toner of the present invention includes a colorant, either a pigment or dye, in a quantity suflicient to impart color to the resin composition, generally in a quantity up to about 25%, by weight, and particularly from about 1% to about by weight, of the toner, whereby the resulting toner will form a clear visible image on a transfer member. Any one of a wide variety of pigments or dyes which do not adversely affect the properties of the toner may be employed to impart color to the resin; e.g., carbon black, a commercial red, blue or yellow dye, and since such dyes and/or pigments are well-known in the art, no detailed enumeration thereof is deemed necessary for a full understanding of the invention.

The colored toner may be prepared by any one of a wide variety of procedures for forming a uniform dispersion of the dye or pigment in the resinous material. Thus, for example, the resinous material and a suitable pigment may be heated and blended on a rubber mill and then allowed to cool and harden to encase the pigment within the resinous material. The pigmented or dyed resinous material is then micronized; e.g., in a jet pulverizer, to

particles having a particle size generally employed for a toner; generally an average particle size of less than about 30 microns, preferably an average particle size from about 10 to about 20 microns. Alternatively, the finely divided toner may be prepared by spray drying a toner composition of the colorant and resin dissolved in a solvent.

The above procedures and other procedures for producing colored toner of the desired particle size are generally known in the art and may be employed for producing the toner of the present invention and therefore, no detailed discussion thereof is necessary for a full understanding of the invention.

The hereinabove described toner of the invention formed from a weakly crosslinked amorphous polymer may also include other materials generally employed for modifying the characteristics of a toner, such as conductive materials to modify the triboelectric properties thereof, magnetic material or the like, and the use of such materials is deemed to be within the scope of those skilled in the art from the teachings herein. Similarly, the toner may include a resinous component other than the hereinabove described weakly crosslinked polymer, provided that at least a major portion of the resinous portion of the toner is comprised of the hereinabove described crosslinked polymer; generally the crosslinked polymer comprises from about to about 100%, preferably from to of the resinous portion of the toner. The remaining portion of the resinous component of the toner, if any, is generally a resin of the type employed to modify the physical properties of a toner material; e.g., a long chain thermoplastic which has little tendency toward agglomeration or cold flow, such as, polyvinyl butyral, polyethylene shellac, waxes, polyesters, polyvinyl acetal, polyvinyl chloride, polyvinyl acetate and the like.

The toner hereinabove described, is employed in a developer composition by loosely coating the toner on a suitable electrostatographic developer carrier surface to which the toner is aflixed by electrostatic attraction, as generally known in the art. Thus, for example, the toner composition may be employed in the cascade development technique, as more fully described in US. Pat. No. 2,618,551 to Walkup, US. Pat. No. 2,618,552 to Wise, and U8. Pat. No. 2,638,416 to Walkup et al. In the cascade development technique, the developer composition is produced by mixing toner composition with a carrier, either electrically conducting or insulating, magnetic or non-magnetic, provided that the carrier material when brought in close contact with the toner composition acquires a charge having an opposite polarity to that of the toner whereby the toner adheres to and surrounds the carrier. Thus, the carrier material is selected in accordance with its triboelectric properties so that the toner is either above or below the carrier material in the triboelectric series, to provide a positively or negatively charged toner.

The carrier particles are larger than the toner particles by at least one order of magnitude of size and are shaped to roll across the latent image-bearing surface. In general, the carrier particles should be of sufiicient size so that their gravitational or momentum force is greater than the force of attraction of the toner particles in the area of the image-bearing surface where the toner particles are retained, whereby the carrier will not be retained by the toner particles which are attracted to the image-bearing surface. The carrier particles generally have a particle size from about 30 to about 1000 microns, but it is to be understood, that the carrier particles may be of a size other than ,as particularly described, provided that the carrier flows easily over the image-bearing surface, without requiring special means for effecting removal of the carrier particles from the image-bearing surface.

The degree of contrast or other photographic qualities in the finished image may be varied by changing the relative proportions of toner and carrier material and the choice of optimum proportions is deemed to be within the scope of those skilled in the art. In general, however, the toner of the invention is employed in amounts to provide Weight ratios of carrier to toner of from about 25:1 to about 250:1, preferably from about 75:1 to about 100:1, to produce a dense readily transferable image.

In addition to the use of particles to provide the carrier surface, the bristles of a fur brush may also be used. Here also, the toner particles acquire an electrostatic charge of polarity determined by the relative position of the toner particles and the fur fibers in the triboelectric series. The toner particles form a coating on the bristles of the fur clinging thereto by reason of the electrostatic attraction between the toner and the fur just as the toner clings to the surface of the carrier particles. The general process of fur brush development is described in greater detail in US. Pat. No. 3,251,706 to L. E. Walkup.

Even more closely related to the cascade carrier development is magnetic brush development. In this process, a carrier is selected having ferromagnetic properties and selected relative to the toner in a triboelectric series so as to impart the desired electrostatic polarity to the toner and carrier as in cascade carrier development. On inserting a magnet into such a mixture of toner and magnetic material the carrier particles align themselves along the lines of force of the magnet to assume a brush-like array. The toner particles are electrostatically coated on the surface of the powder carrier particles. Development proceeds as in regular cascade carrier development on moving the magnet over the surface bearing the electrostatic image so that the bristles of the magnetic brush contact the electrostatic image-bearing surface.

Still another method of carrier development is known as sheet carrier development in which the toner particles are placed on a sheet as of paper, plastic, or metal. This process is described in US. Pat. No. 2,895,847 to C. R. Mayo. As described therein the electrostatic attraction between the sheet surface and toner paritcles necessary to assure electrostatic attraction therebetween may be obtained by leading the sheet through a mass of electroscopic toner particles whereby there is obtained a rubbing or sliding contact between the sheet and the toner. In general, it is desirable to spray the surface of the sheet hearing the electroscopic toner particles with ions of the desired polarity as by the use of a corona charging device as described in the patent of Mayo.

The resulting image of toner particles of the imagebearing surface may then be transferred to a suitable transfer member to form the final copy. The transfer of the toner particles may be effected adhesively or electrostatically as known in the art.

The toner as should be apparent from the hereinabove teachings, may be employed in a wide variety of developer compositions by electrostatically coating the toner composition to a suitable carrier surface, which is subsequently passed over a latent image-bearing surface. The toner of the invention may also be employed for developing an electrostatic latent image formed by other than electrophotographic means; for example, the development of electrostatic latent images formed by pulsing electrodes as employed in electrostatic printing processes. In addition, the toner of the invention may be employed for developing an electrostatic latent image on a surface other than a photoconductive insulating surface. Therefore, the overall invention is not limited to a specific technique for forming or developing an electrostatic latent image or to a specific carrier for the toner.

The toners of the present invention are capable of being fixed to a suitable support medium such as paper to provide a finished copy by the application of pressure; with the particular pressure required for effecting such pressure fixing varying with the particular toner employed. The pressure is preferably provided by pressing the transfer material having the toner image thereon between a pair of polished metal rollers that are in contact with each other under a specified pressure. In general, the roll loading is from about 10 to about 600 pounds per linear inch, and preferably from about 50 to about 400 pounds per linear inch. The roll loading in pounds per linear inch is the total applied force divided by the length of the roll. In some cases, the pressure fixing of the toner to the support medium may be heat asserted; e.g., by the use of a coated or uncoated heated metal roll and an uncoated or elastomeric coated backup roll.

It is to be understood, however, that although the toners of the present invention are particularly suitable for the preparation of a final copy by pressure fixing, such toners may also be fixed by conventional procedures; e.g., heat fusing.

This invention is further illustrated by the following examples but it is to be understood that the scope of the invention is not to be limited thereby. Unless otherwise specified, all parts are by weight.

EXAMPLE I Styrene (10 1b.), n-butyl methacrylate (30 1b.) and benzoyl peroxide are added to a mixture of water lb.) including tricalcium phosphate (1.0 lb.) and Alkanol B (7.26 g.) as emulsifying agent. The mixture is maintained at C. for six hours and cooled to room temperature. 750 ml. of concentrated hydrochloric acid is then added to dissolve the tricalcium phosphate. After agitating for 20 minutes, the mixture is washed with water and dried in air.

The styrene-n-butyl methacrylate copolymer has a styrene content of about 35 mole percent, a number average molecular weight of about 44,000 and a T of 40 C.

The copolymer is dissolved in boiling isopropanol (12 gal.) and potassium hydroxide (4.0 lb.) added thereto while maintaining reflux. After two hours, the mixture is precipitated into a large excess of water and the resulting ionic polymer is washed several times in water and dried at 90 C.

The ionic polymer has a T of 48 C. and 5.1 mole percent potassium ions.

Preparation of toner The ionic polymer (19 parts) is dissolved in tetrahydrofuran parts) and mixed with 1 part Mogul L carbon black. The solvent is evaporated with stirring and final traces removed in a vacuum oven at 80 C. The slab of ionic polymer is then ball milled in a polyethylene jar containing cylindrical stones for four hours and sieved through a 44, grid. The number average particle size iS 9.0;!

Preparation and use of developer The toner is combined with an uncoated glass bead carrier (the glass is comprised of 42.0% PbO; 18.3% TiO 5.6% BaO; 2.3% ZrO and 31.8% SiO- all by weight) to produce a developer having 1 wt. percent of the toner.

The developer is used to develop an electrostatic latent image by cascading the developer (three times) over an electrostatic latent image formed on a flat selenium plate charged to +700 volts. The image is transferred to paper using +700 volts and fixed using 3" bare steel rollers at room temperature with the loading being 400 pounds per linear inch and the roller speed 4.2/ sec.

The fixed image is qualitative (removal of the image required rubber for 4-5 seconds with moderate pressure).

EXAMPLE II N-butyl methacrylate (950 ml.), acrylic acid (50 ml.) and azo-bis(isobutyronitrile) (15 g.) is dissolved in 2.5 l. acetone and refluxed for 15 hours. The solution is concentrated to 50% of its volume and the polymer recovered by precipitation with methanol, followed by extraction with methanol and water. The polymer is filtered and dried at 60 C. The resulting polymer has an acrylic acid content of 5.8 mole percent.

The polymer is then formed into a toner as described in Example I.

The toner is combined as described in Example I with an uncoated glass carrier and used to develop an electrostatic latent image as described in Example I and fixed to a paper as described in Example I.

The fixed image is qualitative.

EXAMPLE HI An n-butyl methacrylate-vinyl N-methyl pyridine copolymer (94/4) prepared by solution polymerization in acetone using azo-bis (isobutyronitrile) initiator is formed into an ionic polymer by neutralization with a solution of methane sulfonic acid.

The ionic polymer is formed into a toner, used to develop an electrostatic latent image and fixed to paper as described in Example I.

The fixed image is qualitative.

EXAMPLE IV An ionic polymer comprised of n-butyl methacrylate, dimethyl aminoethyl methacrylate and acrylic acid (94/ 3/3) is prepared by terpolymerization in acetone solution using azo-bis (isobutyronitrile) initiator.

The ionic polymer is formed into a toner, used to develop an electrostatic latent image and fixed to paper as described in Example I.

The fixed image is qualitative.

EXAMPLE V 2,2,4-trimethyl hexamethyleneadipamide is prepared by solution polymerization using 10 parts of diamine and 9 parts of the adipic acid as described in Condensation Polymers of Interfacial and Solution Methods, P. W. Morgan, Interscience 1965, using an excess of amine for amine termination. An ionic polymer is prepared by neutralization with hydrochloric acid.

A toner is prepared from the ionic polymer as described in Example I.

The fixed image is qualitative.

EXAMPLE VI Diacetone acrylamide g.), n-butyl acrylate (95 g.), acetone (300 ml.) and azo-bis (isobutyronitrile) (2.0 g.) is refluxed overnight, precipitated into methanol, reprecipitated in acetone into methanol and dried in a vacuum oven at 60 C.

The resulting polymer (20 g.) is dissolved in 50 ml. acetone with 1 g. Mogul L carbon black, evaporated to dryness with stirring and dried in a vacuum oven at 60 C. The resulting product is ball milled to produce a pulverized material which passes through a 44 grid.

The resulting toner is used to develop an electrostatic latent image and fixed to paper as described in Example I.

The fixed image is qualitative.

EXAMPLE V11 Polyvinyl acetate-polyvinyl alcohol mole percent) is prepared by partial hydrolysis of polyvinyl acetate.

The polymer (50 g.) is mill rolled with 5 g. carbon black and 5 g. of sodium metaborate at 100 C. to produce a uniform mixture.

The resulting product is jet mieronized with Dry Ice to an average particle size of about 10 microns.

The developer is employed to develop an electrostatic latent image and fixed to paper as described in Example I.

The fixed image is qualitative.

EXAMPLE VIII The n-butyl methacrylate-acrylic acid copolymer which is produced in Example II is neutralized with potassium hydroxide in methanol to produce an ionic polymer with 1.4 mole percent potassium ions (T -46 C.).

The ionic polymer is formed into a toner, used to develop an electrostatic latent image and fixed to paper as described in Example I.

The fixed image is qualitative.

The toners of the present invention are particularly advantageous in that such toners are capable of being fixed to a support in image configuration by the application of pressure, and in addition, possess the structural properties required to withstand the forces encountered in the development process. .The ability to fix a toner image by the application of pressure is advantageous in that pressure fixing, with and without heat assistance, is capable of producing fixed images in shorterperiods of time.

Numerous modifications and variations of the present invention are possible in light of the above teachings and, accordingly, within the scope of the appended claims the invention may be practiced other than as particularly described.

What is claimed is:

1. An electrostatographic toner capable of being fixed to a support medium in image configuration by the application of pressure comprising a finely divided colored resin, said resin comprising an amphorous weakly crosslinked polymer having a crosslink bond strength from about 2 to about 30 kcaL/mole and a glass transition greater than about 20 C., said weakly crosslinked polymer being pressure sensitive, whereby pressure application to said weakly crosslinked polymer results in a polymer having the properties of the uncrosslinked polymer.

2. The toner of claim 1 wherein the glass transition temperature of said weakly crosslinked polymer is from about 20 C. to about 50 C.

3. The toner of claim 1 wherein the weakly crosslinked polymer has a glass transition temperature of from about 20 C. to about 50 C.

4. The toner of claim 1 wherein the weakly crosslinked polymer has a yield stress from about 500 to 20,000 p.s.i.

5. The toner of claim 1 wherein the weakly crosslinked polymer has a yield stress from about 1000 to about 5 000 p.s.i.

6. The toner of claim 1 wherein the weakly crosslinked polymer in its uncrosslinked state resulting from the application of pressure has a glass transition temperature from about 'l00 C. to about 40 C.

7. The toner of claim 1 wherein the weakly crosslinked polymer in its uncrosslinked state resulting from the application of pressure has a glass transition temperature from about -50 C. to about 20 C.

8. The toner of claim 1 wherein the weakly crosslinked polymer is an ionic polymer.

9. The toner of claim 8 wherein the glass transition temperature of the ionic polymer is from about 20 C. to about 50 C. and the yield stress of the ionic polymer is from about 500 to about 20,000 p.s.i.

10. The toner of claim 1 wherein the ionic polymer is formed from a polymer selected from the group consisting of copolymers of styrenes and alkyl acrylates wherein the alkyl group contains 1-12 carbon atoms, copolymers of styrenes and alkyl methacrylates wherein the alkyl group has from 4-12 carbon atoms, copolymers of acrylic acid and alkyl acrylates wherein the alkyl group contains l-12 carbon atoms, copolymers of acrylic acid and alkyl methacrylates wherein the alkyl group contains 4-12 carbon atoms; copolymers of methacrylic acid and alkyl acrylates wherein the alkyl group contains from l-12 carbon atoms; copolymers of methacrylic acid and alkyl methacrylates wherein the alkyl group contains from 4-12 carbon atoms; polymers of vinyl N-alkyl pyridine and alkyl acrylates wherein the alkyl group contains 1-12 carbon atoms; polymers of vinyl N-alkyl pyridine and alkyl methacrylates wherein the alkyl group contains from 4-12 carbon atoms, amine terminated 2,2,4-trimethylhexamethylene adipamide.

11. The toner of claim 1 wherein the weakly crosslinked polymer is a hydrogen bonded polymer.

12. The toner of claim 11 wherein the glass transition temperature of the hydrogen bonded polymer is from 1 1 about 20 C. to about 50 C and the yield stress. is from about 500 to about 20,000 p.s.i. I v

13. The tonerof claim ll wherein the hydro'gen'bonded polymer is formed from a polymer selected from'the group consisting of polymers of acrylic acid and analkyl acrylate wherein the alkyl group contains from 1-12 carbon atoms, polymers of methacrylic 'acid'and analkyl acrylate wherein the alkyl group contains from 112 car'- bon atoms, polymers of acrylic acid and an'alkyl mam acrylate wherein the alkyl group has from 4-'12 carbon atoms, a polymer of methacrylic acid andan alkyl rheth acrylate wherein the alkyl group has from-#1 2 carbon atoms, a polymer of a vinyl alkyl pyridine and analkyl acrylate wherein the alkyl group has l l2"'carbon atoms, a polymer of a vinyl alkyl pyridine and an alkyl methacrylate the alkyl group has 4-12 carbon atoms, poly (N,N-

diisobutylhexamethyleneadipamide) and a p'olymer of diacetone-acrylamide and an alkyl acrylate whereirrthe alkyl group has from 1-12 carbon atoms. 1"

14. The toner of claim 1 wherein the crosslinks of the weakly crosslinked polymer are formed by weak acidweak base associative bonding.

I 15 The toner of claim 14 wherein the glass transition temperature ofthe weakly crosslinked polymer is from about 20" C. to about 50 C. and the yield stress is from abdut500 to about 20,000 p.s;i.

I "16. Thetoner of claim 17 wherein the Weakly crosslinked polymer-is vinyl alcohol-vinyl acetate copolymer admixed with boric acid.

References Cited I UNITED STATES PATENTS J. TRAVIS BROWN, Primary Examiner J. L. GOODROW, Assistant Examiner US. Cl. 'X.R. 

